This invention relates generally to the field of vending machines, and more particularly to an inductive product sensor in an open-access vending machine.
Hotels offer many services for customers staying in their rooms. One service a hotel customer may find in their room is an xe2x80x9copen-access refreshment centerxe2x80x9d or xe2x80x9crefreshment barxe2x80x9d that is pre-stocked with drinks and snacks by the hotel. The hotel charges a per item fee for each refreshment product that is used-by the customer. If the number of refreshment units consumed by the customer is inaccurate or incorrectly counted, then the hotel and the customer will be faced with inappropriate charges to resolve. If there is an undercount, the hotel will lose money. If an overcount occurs, the customer will be overcharged by the refreshment center. Accordingly, it is important for a hotel to be able to track the number of refreshment units a hotel customer has used so the guest is charged correctly.
In contrast to the desire to be able to properly track the number of items used by the customer, there are other features that are desired in a refreshment bar. It is important for customers to have free unobstructed access to the product (e.g., cans). Users are more likely to consume the products if they can just reach into a refrigerator or dispenser unit and take the product without moving a mechanical arm or similar counter mechanism. The accessibility of the product is also enhanced when the product stands upright with the product label facing forward, as opposed to rolling the product container on its side. Also, when a user can view the label, the user is more likely to remove and purchase the item.
It is important, from a manufacturing point of view, to be able to use an inexpensive sensor to count the number of items used. In addition, an inventory system which provides accurate real-time inventory for a refreshment center is very valuable. A real-time reporting system with centralized data collection can alleviate the need to have a stocking person perform inventory control tasks.
Additionally, being able to do electronic inventory control tasks allows a hotel to restock the refreshment centers only when necessary. The hotel know what products need to be restocked based an electronically determined inventory status, and can order only those products needed. This relieves the need for additional product storage at a location other than the vending machines themselves.
Refreshment centers typically comprise a refrigerator, or a dispensing housing including internal shelves to store one or more products for sale. The refreshments stocked may be, for example, canned drinks, bottled drinks, packaged snacks or foods, and similar items. Conventionally, some vending machines have one or more angled shelves configured to dispense cans. The angled shelves facilitate rolling or sliding the remaining product forward when the first one is removed. A switch at the end of the row senses when a guest or customer removes a product. Then a tally is kept of how many items were used by the guest.
Vending machines exist with free-standing product items but they require a switch or optical sensor at each product location. Although it is logical to have a switch at each product location, it can also be costly, particularly if there are many items to be dispensed in the refreshment center. For example, one device uses visible light switches or infra-red switches placed at each product location. Another technique uses capacitance sensors at each product location. This technology is not low cost because there must be many sensors per row. Furthermore, capacitive sensing is sometimes affected by nearby objects such as the refrigerator door or a person""s hand. This can cause problems as to whether the number of product items is counted correctly or not.
It has been recognized that it would be advantageous to develop a product sensor system for inductively sensing products in a vending machine. Additionally, it would be valuable to provide a cost effective sensor which is not interfered with by nearby objects. It is also important to have a sensor system which allows the product items to be free-standing and easily accessible.
The product sensor system includes a support shelf mounted in the refreshment center, which holds the product containers. Sensor loops are arranged on the shelf adjacent to the product containers, and an analysis circuit is connected to an inductance circuit and sensor loops to measure the inductance changes when product containers are removed from the refreshment center. In one embodiment, a signal from the analysis circuit is compared against a signal from a reference oscillation circuit. The magnitude of a measured phase shift between these two signals indicates the number of product cans placed on the sensor loops. These and other features, advantages, and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description, taken in combination with the accompanying drawings.